1. Field of the Invention
The present invention relates to a method of manufacturing an anode active material composed of carbon nanofibers, and an anode and a lithium battery using the anode active material, and, more particularly, to a method of manufacturing an anode active material which is composed of nitrogen-doped porous carbon nanofibers containing a nano-sized metal oxide, and to an anode and a lithium battery using the anode active material.
2. Description of the Related Art
Recently, lithium batteries have been variously utilized in electric vehicles and power storage devices, in addition to uses as main power sources of small electronic devices, such as mobile phones, notebook computers, etc. The usage of lithium batteries which store electrochemical energy is becoming diversified, and the demand for lithium batteries, a decrement in the capacity of which is low despite frequent charge-discharge, is increasing.
As an anode active material presently useful in the lithium batteries, graphite, which is a carbonaceous material with good lifetime properties, is commercially available, but graphite has a very low theoretical capacity of 372 mAh/g, and a solid electrolyte membrane formed on the surface of the active material upon charge-discharge may undesirably cause safety problems of the lithium battery. Thorough research into alternatives to graphite having low capacity and safety problems is ongoing, and the use of, as the anode active material, a metal oxide such as, for example, TiO2, Li4Ti5O12, KNb5O13, Fe2O3, Co3O4, MnO2, MoO2, MoO3, NiO, CuO, etc., wherein an intercalation reaction or a conversion reaction takes place, is being studied.
However, a metal oxide such as TiO2, Li4Ti5O12, KNb5O13, etc., wherein an intercalation reaction occurs, is limited in terms of theoretical capacity, and a metal oxide such as Fe2O3, Co3O4, MnO2, etc., wherein a conversion reaction occurs, is limited in the transfer rate of lithium and may incur volume expansion upon reaction with lithium, thus generating an active material electrically isolated in the electrodes, undesirably resulting in lowered rate capability.
With the goal of solving the above problems, nano-structured materials are widely studied. The nano-structured materials refer to one-, two-, or three-dimensional structured nanomaterials, and may include nanorods, nanowires, nanoflowers, or nanospheres, as proposed by Nano Lett., 9, (2009) 1045, Angew. Chem., Int. Ed., 48 (2009) 1660, J. Phys. Chem. C, 112 (2008) 4836, Chem. Commun. (2006) 2783. Such nano-structured materials may alleviate aggregation or breakage of the active material, thus reducing changes in stress and volume in the electrodes upon charge-discharge, thereby exhibiting battery characteristics including high capacity and high stability. However, the use of an electrode active material having a large surface area may undesirably increase side-reactions with the electrolyte and may decrease energy density per volume.
Hence, the introduction of an anode active material able to achieve a lithium battery having high capacity and high stability is required to solve such problems.